Method of real time hybrid ARQ

ABSTRACT

A method of wireless communication. The method includes the step of transmitting at least a first sub-frame from a first voice frame. If the first sub-frame is received by the wireless unit, an acknowledgement message is transmitted, and the remaining sub-frames from that voice frame are not transmitted. If the first sub-frame is not received by the wireless unit, however, a non-acknowledgement message is transmitted. Here, the base station retransmits at least another sub-frame from the first voice frame.

BACKGROUND OF THE INVENTION

[0001] I. FIELD OF THE INVENTION

[0002] The present invention relates to telecommunications, and moreparticularly, to wireless communications.

[0003] II. Description of the Related Art

[0004] Wireless communications systems provide wireless service to anumber of wireless or mobile units situated within a geographic region.The geographic region supported by a wireless communications system isdivided into spatially distinct areas commonly referred to as “cells.”Each cell, ideally, may be represented by a hexagon in a honeycombpattern. In practice, however, each cell may have an irregular shape,depending on various factors including the topography of the terrainsurrounding the cell. Moreover, each cell is further broken into two ormore sectors. Each cell is commonly divided into three sectors, eachhaving a range of 120 degrees, for example.

[0005] A conventional cellular system comprises a number of cell sitesor base stations geographically distributed to support the transmissionand reception of communication signals to and from the wireless ormobile units. Each cell site handles voice communications within a cell.Moreover, the overall coverage area for the cellular system may bedefined by the union of cells for all of the cell sites, where thecoverage areas for nearby cell sites overlap to ensure, where possible,contiguous communication coverage within the outer boundaries of thesystem's coverage area.

[0006] Each base station comprises at least one radio and at least oneantenna for communicating with the wireless units in that cell.Moreover, each base station also comprises transmission equipment forcommunicating with a Mobile Switching Center (“MSC”). A mobile switchingcenter is responsible for, among other things, establishing andmaintaining calls between the wireless units, between a wireless unitand a wireline unit through a public switched telephone network(“PSTN”), as well as between a wireless unit and a packet data network(“PDN”), such as the Internet. A base station controller (“BSC”)administers the radio resources for one or more base stations and relaysthis information to the MSC.

[0007] When active, a wireless unit receives signals from at least onebase station or cell site over a forward link or downlink and transmitssignals to at least one cell site or base station over a reverse link oruplink. There are many different schemes for defining wireless links orchannels for a cellular communication system. These schemes include, forexample, time-division multiple access (“TDMA”), frequency-divisionmultiple access (“FDMA”), and code-division multiple access (“CDMA”)type-designs.

[0008] In a CDMA scheme, each wireless channel is distinguished by adistinct channelization code (e.g., spreading code, spread spectrum codeor Walsh code) that is used to encode different information streams.These information streams may then be modulated at one or more differentcarrier frequencies for simultaneous transmission. A receiver mayrecover a particular stream from a received signal using the appropriateWalsh code to decode the received signal.

[0009] Wireless communications systems employ a number of geographicallydistributed, cellular communication sites or base stations. Each basestation supports the transmission and reception of communication signalsto and from stationary or fixed, wireless communication devices orunits. Each base station handles communications over a particular regioncommonly referred to as a cell/sector. The overall coverage area for awireless communications system is defined by the union of cells for thedeployed base stations. Here, the coverage areas for adjacent or nearbycell sites may overlap one another to ensure, where possible, contiguouscommunications coverage within the outer boundaries of the system.

[0010] When active, a wireless unit receives signals from at least onebase station over a forward link or downlink and transmits signals to atleast one base station over a reverse link or uplink. Several approacheshave been developed for defining links or channels in a cellularcommunication system, including, for example, TDMA (time-divisionmultiple access), and CDMA (code-division multiple access).

[0011] In TDMA communication systems, the radio spectrum is divided intotime slots. Each time slow allows only one user to transmit and/orreceive. Thusly, TDMA requires precise timing between the transmitterand receiver so that each user may transmit their information duringtheir allocated time.

[0012] In CDMA communications systems, different wireless channels aredistinguished by different channelization codes or sequences. Thesedistinct channelization codes are used to encode different informationstreams, which may then be modulated at one or more different carrierfrequencies for simultaneous transmission. A receiver may recover aparticular stream from a received signal using the appropriate code orsequence to decode the received signal.

[0013] For voice applications, conventional cellular communicationsystems employ dedicated links between a wireless unit and a basestation. Voice communications are delay-intolerant by nature.Consequently, wireless units in wireless cellular communication systemstransmit and receive signals over one or more dedicated links. Here,each active wireless unit generally requires the assignment of adedicated link on the downlink, as well as a dedicated link on theuplink.

[0014] With the explosion of wireless telephony, however, a growingconcern for cellular service providers has been voice quality. As thenumber of wireless users has continued to blossom, the demands on thesystem by increasing voice capacity have forced a degradation of thevoice quality each user may experience. For the purposes of the presentdisclosure, reference to voice capacity also includes circuit switchedservices similar to voice, such as video, for example. Moreover, asvoice capacity is increased to support an ever-larger number of wirelessusers, additional issues, including, for example, uplink interferencebetween these users in a single sector may also surface. A tradeoffexists, therefore, between voice quality and voice capacity.

[0015] Consequently, a demand exists for increasing voice qualitywithout unduly influencing the voice capacity of the base station.

SUMMARY OF THE INVENTION

[0016] The present invention provides a method of increasing voicequality without unduly influencing the voice capacity of the basestation. More particularly, the present invention provides a method ofretransmission for one or more voice frames by employing a number ofsub-frames. Within the context of the present invention, each voiceframe may comprise a plurality of sub-frames. It should be noted thatthe method of the present invention may be applicable on both the uplinkand the downlink.

[0017] In one exemplary embodiment of the present invention, at least afirst sub-frame of a plurality of sub-frames formed from a first voiceframe may be transmitted. If an acknowledgement message is received inresponse to transmitting the first sub-frame, the transmission of anyremaining sub-frames from the first plurality may be terminated. If anon-acknowledgement message is received in response to transmitting thefirst sub-frame, a second sub-frame is transmitted. The second sub-framemay comprise a copy of the first sub-frame and/or redundant information.Thereafter, another sub-frame from another voice frame may betransmitted. This another sub-frame may be transmitted in response toreceiving an acknowledgement message corresponding with the first voiceframe and/or a time-out. For the purpose the present disclosure, atime-out may occur if the retransmission scheme corresponding with thevoice frame fails by the passage of a time interval.

[0018] In another exemplary embodiment of the present invention, aplurality of sub-frames may be formed from a voice frame. Here, thevoice frame may be coded. The coded voice frame may then be divided intoa number of sub-frames. Thereafter, the sub-frames may be interleavedindependently.

[0019] In another exemplary embodiment of the present invention, anacknowledgement message may be transmitted in response to receiving afirst sub-frame of a first plurality of sub-frames formed from a firstvoice frame. If an acknowledgement message is transmitted, the remainingsub-frames of the first plurality may not be received. However, if thefirst sub-frame is not received, a non-acknowledgement message may betransmitted. In response to transmitting the non-acknowledgementmessage, a second sub-frame of the first plurality may be received.Consequently, the first voice frame may be decoded by combining thefirst sub-frame and second sub-frame of the first plurality. Thereafter,another sub-frame of another plurality from another voice frame may bereceived.

[0020] In another exemplary embodiment of the present invention, atleast a first sub-frame from a first voice frame is transmitted by abase station. If the first sub-frame is received by a wireless unit, anacknowledgement message may be transmitted. Consequently, the remainingsub-frames from that voice frame may not be transmitted. However, if thefirst sub-frame is not received by the wireless unit, anon-acknowledgement message is transmitted. The base station may thentransmit at least another sub-frame from the first voice frame.

[0021] These and other embodiments will become apparent to those skilledin the art from the following detailed description read in conjunctionwith the appended claims and the drawings attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be better understood from reading thefollowing description of non-limiting embodiments, with reference to theattached drawings, wherein below:

[0023]FIG. 1 depicts an embodiment of the present invention;

[0024]FIG. 2 depicts another embodiment of the present invention;

[0025]FIG. 3 depicts another embodiment of the present invention;

[0026]FIG. 4 depicts an aspect of the present invention;

[0027]FIG. 5 depicts a flow chart of an embodiment of the presentinvention;

[0028] FIGS. 6(a) and 6(b) each depict a table illustrating aspects ofthe present invention;

[0029]FIG. 7 depicts an aspect of the present invention;

[0030]FIG. 8 depicts an aspect of the present invention;

[0031]FIG. 9 depicts an aspect of the present invention;

[0032]FIG. 10 depicts an aspect of the present invention;

[0033]FIG. 11 depicts an aspect of the present invention;

[0034]FIG. 12 depicts an aspect of the present invention; and

[0035]FIG. 13 depicts an aspect of the present invention.

[0036] It should be emphasized that the drawings of the instantapplication are not to scale but are merely schematic representations,and thus are not intended to portray the specific dimensions of theinvention, which may be determined by skilled artisans throughexamination of the disclosure herein.

DETAILED DESCRIPTION

[0037] In current wireless systems employing the CDMA-based technology,voice frame transmission time may be fixed at intervals of time. Forexample, in CDMA 2000 1x, the voice frame transmission time may be 20ms. A full rate, half (½) rate, quarter (¼^(th)) rate or a one-eighth(⅛^(th)) rate frame may be transmitted every interval—e.g., every 20ms—on both the downlink and the uplink. Consequently, a low frame errorrate (“FER”) is targeted (e.g., 1% FER) to avoid compromising voicequality.

[0038] The capacity of wireless spread spectrum systems may be radiofrequency (“RF”) limited. For example, a low FER of 1% may not beguaranteed in the presence of large number of users. Here, users on theuplink may interfere with one another due to the non-orthogonal natureof the uplink using CDMA-based technology. This RF limitation may alsohappen on the downlink because of insufficient power available at thebase station necessary to reach a user(s) having a low FER of 1%, forexample. Therefore, the system voice capacity may be severely limited.

[0039] In view of the above, the present invention provides a method ofincreasing voice quality without unduly influencing the voice capacityof the base station. More particularly, the present invention provides amethod of retransmission for each voice frame that may be used on theuplink and/or the downlink, for example. Within the context of thepresent invention, each voice frame may comprise a number of sub-frames.The method may include, for example, transmitting (e.g.,re-transmitting) a subsequent sub-frame within a voice frame if aninitial sub-frame is not received. The reception of the initialsub-frame may be determined by the transmission of an acknowledgementmessage(s) (“ACK”) or non-acknowledgement (“NACK”) message(s).Consequently, the RF limitation detailed herein may be overcome byallowing the use of a simple real-time retransmission scheme, such asautomatic repeat request (“ARQ”) or Hybrid ARQ, for example. As aresult, the method supports targeting the first transmission at a higherFER than 1%, for example.

[0040] The present invention provides a real time retransmission scheme,such as hybrid ARQ. In so doing, the method promotes increased voicecapacity from efficient utilization of the available power in the basestation. Moreover, the method advances reduced intercell and intracellinterference, thereby increasing the system capacity further.

[0041] In one embodiment of the present invention, the method includestransmitting at least a first sub-frame of a plurality of sub-framesformed from a first voice frame. If an acknowledgement message (“ACK”)is received in response to transmitting the first sub-frame, thetransmission of any remaining sub-frames from the first plurality may beterminated. If a non-acknowledgement (“NACK”) message is received inresponse to transmitting the first sub-frame, a second sub-frame istransmitted (e.g., re-transmitted). The second sub-frame may comprise acopy of the first sub-frame and/or redundant information.

[0042] Once the first voice frame is transmitted, retransmitted,received or not received, another sub-frame from another voice frame maybe subsequently transmitted. This subsequent sub-frame from anothervoice frame may be transmitted in response to receiving an ACK. This ACKmessage may correspond with the first voice frame and/or a time-outassociated with retransmitting first voice frame. For the purpose thepresent disclosure, a time-out may occur if the retransmission schemecorresponding with the voice frame fails by the passage of a timeinterval.

[0043] In another embodiment of the present invention, the methodincludes forming a plurality of sub-frames from a voice frame. Here, thevoice frame may be initially coded. The coded voice frame may be thendivided into a number of sub-frames. Thereafter, the sub-frames may beinterleaved independently.

[0044] In another embodiment of the present invention, the methodincludes transmitting an acknowledgement (“ACK”) message in response toreceiving a first sub-frame of a first plurality of sub-frames formedfrom a first voice frame. If an ACK message is transmitted, thereception of the remaining sub-frames of the first plurality may not beterminated. However, if the first sub-frame is not received, anon-acknowledgement (“NACK”) message may be transmitted. In response totransmitting the NACK message, a second sub-frame of the first pluralitymay be received. Consequently, the first voice frame may be decoded bycombining the first sub-frame and second sub-frame of the firstplurality.

[0045] Once the first voice frame is transmitted, retransmitted,received or not received, another sub-frame from another voice frame maybe subsequently transmitted. This subsequent sub-frame from anothervoice frame may be transmitted in response to receiving an ACK message.This ACK message may correspond with the first voice frame and/or atime-out associated with retransmitting first voice frame. For thepurpose the present disclosure, a time-out may occur if theretransmission scheme corresponding with the voice frame fails by thepassage of a time interval.

[0046] In another embodiment of the present invention, the methodincludes transmitting at least a first sub-frame from a first voiceframe by a base station. If the first sub-frame is received by awireless unit, an ACK message may be transmitted. Consequently, theremaining sub-frames from that voice frame may not be transmitted.However, if the first sub-frame is not received by the wireless unit, aNACK message is transmitted. The base station then may transmit (e.g.,re-transmit) at least another sub-frame from the first voice frame.

[0047] Referring to FIG. 1, an embodiment of the present invention of aretransmission scheme is shown. More particularly, FIG. 1 depicts ahybrid ARQ operation for the downlink. Each exemplary voice frame may beset to 20 ms and divided into four 5 ms sub-frames, as supported by CDMA2000 1x. Here, two users may share the same frame by means of the sameWalsh code in a time-multiplexed fashion.

[0048] In the embodiment illustrated in FIG. 1, a first user maytransmit its first sub-frame in the first depicted 5 ms sub-frame.Similarly, a second user may transmit its first sub-frame in the seconddepicted 5 ms sub-frame. After transmitting the first sub-frame, bothfirst and second users wait for the ACK/NACK feedback from the receiver.If an ACK is received, the second sub-frame may not transmitted (e.g.,DTX'ed). In the example of FIG. 1, the first user receives a NACK andconsequently retransmits the sub-frame in the third 5 ms sub-frame. Incontrast, the second user receives an ACK and is DTX'ed (e.g., theretransmission of the second sub-frame may be aborted).

[0049] For downlink retransmission schemes, such as HARQ, an ACK/NACKfeedback may be provided by stealing the transmit power control (“TPC”)bits. For example, stealing one (1) or two (2) bits for every 20 msinterval may have a negligible impact on the power control of thesystem. It should be noted that all sectors in an active set receivingan ACK may not receive the second sub-frame transmission (e.g., DTX'ed).For the purposes of the present disclosure, an active set may consist ofsector(s) with which each user may be in communication simultaneously.

[0050] Referring to FIG. 2, an embodiment of the present invention of aretransmission scheme is shown. More particularly, FIG. 2 depicts ahybrid ARQ operation for the uplink. In the uplink direction, Walshcodes are not shared across the users. A frame of 20 ms, for example,may be divided into two 7.5 ms frames and one 5 ms inter sub-frame gap.Here, a user may retransmit in the second sub-frame if a NACK isreceived from the base station.

[0051] For RL HARQ operation, an ACK/NACK feedback may be provided onthe FL through a channel, such as the common power control channel(“CPCCH”), for example. Different users may be allocated different bitpositions in the exemplary CPCCH slot. It is also possible here to stealTPC bits for use in providing ACK/NACK feedback. For example, stealingone (1) or two (2) bits for every 20 ms interval may have negligibleimpact on power control. Users in simplex (e.g., communicating with asingle sector) may decode an ACK from the serving cell, while users in asoft handoff (“SHO”) may try to decode ACK signal from all the sectorsin the active set. The second sub-frame transmission is not transmitted(e.g., DTX'ed) if at least one sector positively acknowledges the firstsub-frame.

[0052] Transmissions from different users may be offset by an integernumber of slots, as shown in FIG. 3. This allows for the avoidance ofoverlapping sub-frames from different users and may maximize the benefitfrom DTX'ing the second sub-frame. It should also be noted that DTX'ingat the second sub-frame on the downlink may make a greater base stationpower fraction (e.g., E_(c)/I_(or)) available for other users, whileDTX'ing on the uplink may reduce both intra-cell and inter-cellinterference.

[0053] Real Time Retransmission

[0054] In the present invention, the maximum number of retransmissionattempts may be limited so to restrict the total transmission times. Inexamples described herein, a maximum frame recovery time may be, forexample, 20 ms.

[0055] Referring to FIGS. 4 and 5, an aspect of the present invention isdepicted in conjunction with a flow chart of an embodiment of thepresent invention. As shown, a voice frame is initially coded and thendivided into a first sub-frame (#1) and a second sub-frame (#2).Sub-frames #1 and #2 may then interleaved independently. Subsequently,the transmitter first sends sub-frame #1 and then waits for an ACK/NACKfrom the receiver. The second sub-frame may then be transmitted only ifa NACK is received. The receiver may then try to decode the voice frameby combining sub-frame #1 and sub-frame #2. To assist in the decodingoperation, the sub-frame #2 may contain redundant information and/or acopy of sub-frame #1.

[0056] It should be noted that the 20 ms frame transmission time limitand the two sub-frame transmissions are exemplary aspects of the method.These aspects are used merely for illustrative purposes. Consequently,the principles of this method may be applied to cases for other than 20ms transmission times, as well as for the case where more than twosub-frames are employed.

[0057] Modulation and coding tables for uplink and downlink Hybrid ARQare shown in FIGS. 6(a) and 6(b), respectively. It should be noted thatthe coding rate on the uplink may be the same for both sub-frame #1 andsub-frame #2—e.g., the second sub-frame #2 may be an exact copy of thefirst sub-frame #1. However, for the downlink Hybrid ARQ, the codingrate after receiving the second sub-frame may be different from thecoding rate obtained with sub-frame#1—e.g., incremental redundancyHybrid ARQ.

[0058] As the uplink may not be Walsh code limited, a more robustmodulation and coding might always be chosen. This is a consequence ofthe uplink using length 16 Walsh codes, for example. However, a lessrobust modulation and coding may be required on the downlink becausehigher length Walsh codes are used, as shown in FIG. 6(b).

[0059] Uplink Operation

[0060] In the uplink direction, a wireless unit first transmits thefirst sub-frame. Thereafter, the wireless unit waits for an ACK/NACKfeedback response from the base stations in its active set. The secondsub-frame may then be transmitted only if a NACK is received from allthe base stations, as depicted by example in FIG. 9. If an ACK isreceived from at least one base station, however, the second sub-framemay not be transmitted. This scenario is illustrated in FIGS. 7 and 8.In circumstance where the wireless unit is in communication with onlyone base station, the ACK/NACK feedback is provided from this singlebase station.

[0061] Downlink Operation

[0062] In the downlink direction, sub-frames may be transmitted from allthe sectors in the user's active set. Each sector may transmit the firstsub-frame and thereafter waits for an ACK/NACK from the wireless unit. Asector may then transmit the second sub-frame if a NACK is received fromthe wireless unit, as shown by example in FIG. 11. Otherwise, if an ACKis received, the second sub-frame may not be transmitted. This scenariois illustrated in FIG. 10.

[0063] In case of ACK to NACK error at some sectors, the secondsub-frame may be transmitted from the base station receiving the NACK.This scenario is illustrated in FIG. 12. On the other hand, in case ofNACK to ACK error, the second sub-frame may not be transmitted from thesector receiving an ACK, as shown in FIG. 13. The voice frame may stillbe received successfully if some of the sectors not making the NACK toACK error, however, retransmit the second sub-frame.

[0064] While the particular invention has been described with referenceto illustrative embodiments, this description is not meant to beconstrued in a limiting sense. It is understood that although thepresent invention has been described, various modifications of theillustrative embodiments, as well as additional embodiments of theinvention, will be apparent to one of ordinary skill in the art uponreference to this description without departing from the spirit of theinvention, as recited in the claims appended hereto. Consequently, themethod, system and portions thereof and of the described method andsystem may be implemented in different locations, such as the wirelessunit, the base station, a base station controller and/or mobileswitching center. Moreover, processing circuitry required to implementand use the described system may be implemented in application specificintegrated circuits, software-driven processing circuitry, firmware,programmable logic devices, hardware, discrete components orarrangements of the above components as would be understood by one ofordinary skill in the art with the benefit of this disclosure. Thoseskilled in the art will readily recognize that these and various othermodifications, arrangements and methods can be made to the presentinvention without strictly following the exemplary applicationsillustrated and described herein and without departing from the spiritand scope of the present invention It is therefore contemplated that theappended claims will cover any such modifications or embodiments as fallwithin the true scope of the invention.

1. A method of wireless communication comprising: transmitting at leasta first sub-frame from a first voice frame; and retransmitting at leasta first sub-frame from the first voice frame in response to receiving anon-acknowledgement message.
 2. The method of claim 1, wherein thesecond sub-frame comprises at least one of a copy of the first sub-frameand redundant information.
 3. The method of claim 1, further comprising:forming a first plurality of sub-frames from the first voice frame, thefirst plurality comprising the first and second sub-frames.
 4. Themethod of claim 3, wherein the step of forming a first plurality ofsub-frames comprises: coding the first voice frame; and dividing thefirst coded voice frame into the first plurality of sub-frames.
 5. Themethod of claim 4, wherein the step of forming a first plurality ofsub-frames further comprises: interleaving the first plurality ofsub-frames independently.
 6. The method of claim 4, further comprising:terminating transmitting of any remaining sub-frames from the firstplurality in response to receiving an acknowledgement message.
 7. Themethod of claim 1, further comprising: transmitting at least anothersub-frame from another voice frame in response to at least one ofreceiving an acknowledgement message and a time-out condition.
 8. Themethod of claim 7, wherein the acknowledgement message is received inresponse to the receipt of one of the sub-frames of the first plurality.9. The method of claim 8, further comprising: forming the at leastanother plurality of sub-frames from the another voice frame, the stepof forming another plurality of sub-frames comprises: coding the firstvoice frame; and dividing the first coded voice frame into the firstplurality of sub-frames.
 10. A method of wireless communicationcomprising: transmitting an acknowledgement message in response toreceiving a first sub-frame of a first plurality of sub-frames formedfrom a first voice frame.
 11. The method of claim 10, furthercomprising: transmitting a non-acknowledgement message in response tofailing to receive the at least first sub-frame.
 12. The method of claim11, further comprising: receiving at least a second sub-frame of thefirst plurality in response to transmitting a non-acknowledgementmessage.
 13. The method of claim 12, further comprising: decoding thefirst voice frame by combining the first sub-frame and second sub-frameof the first plurality.
 14. The method of claim 13, wherein the secondsub-frame of the first plurality comprises at least one of a copy of thefirst sub-frame and redundant information.
 15. The method of claim 11,wherein the first plurality of sub-frames is formed by coding the firstvoice frame and dividing the first coded voice frame into a firstplurality of sub-frames.
 16. The method of claim 11, further comprising:receiving at least another sub-frame of another plurality from anothervoice frame in response to receiving an acknowledgement message.
 17. Themethod of claim 16, further comprising: terminating receiving anyremaining sub-frames of the first plurality in response to transmittingan acknowledgement message.
 18. A method of wireless communicationcomprising: forming a plurality of sub-frames from a voice frame, thestep of forming a plurality of sub-frames comprising: coding the firstvoice frame; and dividing the first coded voice frame into the firstplurality of sub-frames.
 19. The method of claim 18, further comprising:interleaving the first plurality of sub-frames independently.